It is known in the prior art that information can be stored in the form of charge on a capacitor having an insulator layer with respective metal or semiconductor electrodes on the opposite faces thereof. A memory system based on stored charge is attractive for computer technology because of the small number of components required for storage of each bit of information. The stored information in the form of charge on the capacitor will last for an indefinite period of time if the associated circuitry does not cause the stored charge to decay by a leakage of charge from the capacitor. Heretofore, convenient technology was not known which could be used to charge and discharge the storage capacitor without introducing a large amount of leakage current. It is desirable to have a technology for rapidly charging and discharging a storage capacitor so that a simple and small non-volatile random access memory could be produced or fabricated using charge storage. One known system for charging and discharging a capacitor involves the use of diodes with low reverse leakage current in the charging and discharging circuit paths. A dielectric diode provided in accordance with the principles of this invention has a sufficiently low leakage current to permit it to be used successfully in combination with a capacitor to form a non-volatile charge store memory cell or unit.
The nature and function of illustrative background literature which is of general interest for the practice of this invention is presented as follows:
A. D. Kahng and S. M. Sze, "A Floating Gate and Its Application to Memory Devices," The Bell System Technical Journal Vol. 46, No. 6, July-August, 1967, pp. 1288-1295. Kahng and Sze describe a non-volatile semiconductor memory utilizing charge storage on a capacitor in the form of a floating or unconnected gate electrode. Charge is applied to this floating gate by the injection of electrons from an auxiliary electrode, through an insulating layer, and onto the floating gate. It is necessary that electrons are more easily injected from the first electrode, through the insulator, to the second electrode, than they are from the floating gate to the third electrode. It is postulated by Kahng and Sze that this condition can be met by making the energy barrier on the insulator between the first two electrodes greater than that on the insulator between the floating gate and the third electrode. However, Kahng and Sze do not disclose the use of a dielectric diode with low reverse leakage as an integral part of the floating gate memory cell. The charge retention time of the device of Kahng and Sze is short, because of the leakage of current from the storage capacitor through the insulator and back to the electrode used for charging the capacitor, and is insufficient for a capacitor memory cell with a long charge retention time.
b. R. Williams, "Photoemission of Electrons from Silicon into Silicon Dioxide: Effects of Iron Migration in the Oxide", Journal of Applied Physics, Vol. 37, No. 4, Mar. 15, 1966, pp. 1491-1494. Williams describes experiments done on the system Si--SiO.sub.2 --Au in a sandwich structure. He introduced sodium ions into the SiO.sub.2 by electrolytically depositing them onto the silicon surface. He found that there resulted an enhanced photoemission from the silicon surface due to the presence of sodium ions. He describes this in terms of a change in the silicon itself which produces the enhanced photoemission. Further, it has been determined in considerations for this invention that when a structure as shown by Williams is either forward-biased or backward-biased dielectric diode behavior cannot be obtained. The structure described by Williams is not a dielectric diode because the contact barrier on the silicon is not significantly different from that on the counter electrode. The contact barrier on the silicon is about 2.9 eV while the contact barrier on the gold is about 3.8 eV. Since both barriers are high and not greatly different, the rectification of this unit is insignificant. Williams does not disclose either the fabrication or the operation of a rectifying device. Further, the noted structure of R. Williams is not stable because the sodium atoms migrate freely at room temperature and change the characteristics of the structure. The sodium migrates from the silicon surface of the aluminum electrode and lowers the contact barrier thereat and changes the directionality of the structure.